NewsJuly 10, 2013

Massive Iceberg Breaks off Pine Island Glacier in Antarctica

Michael D. Lemonick

By Michael D. Lemonick

An enormous slab of ice, about a quarter the size of Rhode Island and some 200 feet thick, has broken away from Antarctica, according to German researchers.

The event, which was recorded by radar aboard Germany’s orbiting TerraSAR-X satellite, was not unexpected. In 2011, a NASA satellite noted that a huge crack had appeared in the ice shelf at the outlet of the frozen continent’s Pine Island Glacier. “At some point, it had to happen,” said Angelika Humbert, a glaciologist at the Alfred Wegener Institute in Bremerhaven, Germany, in an interview. “It’s a very normal process.” 


In fact, as Humbert noted, comparable calving events have happened here before —in 2001 and 2007 and “probably many times before that, although we didn’t have satellites in place to see it,” she said.

It’s not even the largest such event: a slab of ice nearly the size of Connecticut broke away from the Ross Ice Shelf in 2000, and floated around for a decade before it finally broke up. Strictly speaking, therefore, scientists can’t lay the blame for this breakup on global warming.

But global warming is clearly having a huge effect on the Pine Island Glacier itself, a massive river of ice that drains about 10 percent of the West Antarctic Ice Sheet.

This new iceberg won’t raise sea level at all, since it was already floating when it broke away. If the entire sheet were to melt or slide into the ocean, however, sea level would go up by 11 feet — and while that's not likely to happen soon, the combination rising air and water temperatures is destabilizing the ice, both from above and from below.

Of the two, melting from below could prove more problematic. Massive glaciers like the Pine Island grind their way downhill against underlying bedrock, and when they reach the sea, they keep grinding against the seafloor until the water becomes deep enough for the end to start floating.

The transition from grinding to floating is known as the grounding line, and as warm water eats at the ice from below, that line moves back toward the land. That means more floating and less grinding, and the reduced friction can allow the glacier itself to flow faster.

And in fact, Humbert said, “(The Pine Island Glacier) has been melting underneath the entire tongue of ice, and in particular close to the grounding line. “

At the same time, satellite observations have noted that the glacier has been accelerating in its flow to the sea.

The new iceberg, so big that it’s more properly described as an ice island — broke off more than 50 miles from the grounding line, and can’t be directly related to the melting happening there.

But that’s partly because scientists don’t fully understand glacier dynamics, said Humbert. Changes in the velocity of ice flow, she explained, can have effects on the entire glacier.

“You have a lot of stresses in there, which have an effect on calving,” she said. “We’re seeing a change in the entire system. We’re continuing to investigate what’s going on.” 

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